Repetition-dependent acute cardiopulmonary responses during intensity-matched squats in males

The 'strength-endurance continuum' is a key concept in strength training (ST). Although cardiopulmonary responses have seldom been reported in conjunction with ST, this repeated-measurement study examined acute blood pressure and haemodynamic responses continuously depending on the number of repetitions but without changing the intensity. Fifteen healthy male participants (21.6 (2.0) years; mean (SD)) performed an incremental exercise test and a 3-repetition maximum test (3-RM) on a Smith machine. They were then randomly assigned to three ST sessions involving 10, 20 and 30 repetitions at 50% of their 3-RM. Blood pressure (vascular unloading technique) and cardiopulmonary responses (spirometry and impedance cardiography) were continuously monitored. Heart rate (121 (10) vs. 139 (22) vs. 153 (13) bpm, P = 0.001, respectively), cardiac output (10.4 (1.9) vs. 13.6 (3.8) vs. 14.6 (3.1) L/min, P = 0.001, respectively) and diastolic blood pressure (113 (8) vs. 116 (21) vs. 135 (22) mmHg, P = 0.001, respectively) increased in the training sessions with higher repetitions. Stroke volume, systolic blood pressure and end-diastolic volume indicated no change in peak values between training sessions. Total peripheral resistance (13.6 (2.8) vs. 11.3 (3.6) vs. 11.2 (3.1) mmHg min/L, P = 0.002, respectively) was significantly lower with 20 and 30 repetitions, while oxygen uptake ( ${\dot{V}}_{O_2}$ : 15.5 (1.9) vs. 20.5 (4.1) vs. 20.6 (4.4) mL/min/kg, P = 0.001, respectively) was significantly higher. ST of moderate intensity with an exhausting number (>20) of repetitions induces strong haemodynamic responses, especially high cardiac afterload and a compensatory heart rate acceleration, which may also create a strong stimulus for cardiopulmonary adaptation.